This invention relates to a novel porphyrinate and amine composition, which is useful as a catalyst in preparing alkylene carbonates.
Alkylene carbonates are useful in the preparation of polymers and glycols and as solvents.
The preparation of alkylene carbonates by reacting an alkylene oxide and carbon dioxide is well-known. The general conditions for the reaction are the use of temperatures in the approximate range of 100.degree. C.-250.degree. C. Superatmospheric pressures of about 10-300 atmospheres are employed. A reaction temperature of about 160.degree. C.-200.degree. C. and a pressure of 50-150 atmospheres are usually preferred. The reactants are used in about equal molar proportions with the carbon dioxide normally in slight excess.
Known catalysts for the reaction include inorganic bases such as sodium hydroxide and sodium carbonate and organic nitrogen bases such as tertiary amines, quaternary ammonium bases, and salts of these nitrogen bases such as their carbonates and halides. For example, aliphatic tertiary amines such as trimethylamine, aromatic tertiary amines such as pyridine and quinoline, quaternary ammonium hydroxides such as tetraethyl ammonium hydroxide, trimethylbenzyl ammonium hydroxide, dialkyl piperidinium hydroxide, and the carbonates, bicarbonates, and halides of such hydroxides are all known to catalyze the reaction. Catalyst concentrations of 0.1-5 percent based on the weight of alkylene oxide are conventional.
Other catalysts disclosed in the patent literature are anion-exchange resins containing quaternary ammonium chloride groups (U.S. Pat. No. 2,773,070), hydrazine or the hydrohalide salt thereof (U.S. Pat. No. 3,535,341) and guanidine and its salts (U.S. Pat. No. 3,535,342). Catalysts known to the art generally are effective for the purpose and they provide fairly high conversions of the reactants and generally good yields of the desired cyclic carbonates. These yields usually are about 70-90 percent of the theoretical. The latter two patents claim conversions and yields each in excess of 95 percent.
In commercial processes the ammonium halide and anion-exchange resins containing the ammonium halides are the most common catalysts.
There are several problems with the above-described processes. The alkylene carbonates prepared by such processes contain troublesome impurities. Some of these impurities result in a colored product. Further, it has been found that the anion-exchange resin catalysts tend to lose their catalytic activity over a period of use.
A process for the preparation of alkylene carbonates in which the catalyst has long lifetimes, can be recovered easily and repeatedly used, is desirable. Further, a catalyst which does not degrade to form undesirable impurities is needed.